Adjusting the drive ratio on your supercharger allows you to create more or less boost based on the type of operating conditions you expect. Small block 6-71 kits are supplied standard with supercharger pulleys which will provide 12% underdrive. Big block kits are supplied with a 9% underdrive. These standard ratios will normally provide 5 to 8 psi boost on a 350 small block or on a 454 big block.
Note: top and bottom supercharger pulleys are interchangeable.